1. Field of the Invention
This invention relates generally to gauging devices used in determining the amount of liquid in large tanks, and more particularly to a bob with an extended tail portion having exact tape measure graduations which when connected to the measuring tape will overlap the connection to provide consecutive continious and coincident measurement graduations.
2. Brief Description of the Prior Art
In many industries it is necessary to maintain large quantities of liquid material in storage prior to processing or distribution. This is particularly true of the petroleum industry in the oil fields, at the refineries, and at the distribution points. These liquid petroleum stocks are stored in large tanks which may be of thousands of gallons capacity. It is important in the operation of this industry that the quantity of material within these tanks be known with a reasonable degree of accuracy. This information has been furnished in the prior art by dropping a plumb bob on the end of a scale tape into the tank to determine the height of liquid therein. Knowing the physical dimensions of the tank, the quantity of liquid can be calculated by simple mathematics.
In some cases, it is expedient to drop the bob to the bottom of the tank and read the tape at the point where the wetting stops. For this purpose an innage bob is used inasmuch as the result is the amount of material in the tank. In other cases, however, it is more expeditious to drop the bob to the surface of the liquid and determine the distance from the top of the tank to the surface of the liquid. For this purpose an outage bob is used, the result being the amount of material that can be accommodated in that tank. This value can be subtracted from the known total capacity of the tank to determine the amount of liquid in the tank.
In tanks of this type, water is continually condensed from the air above the liquid within the tank because of the fluctuating air temperature. The water accumulates on the bottom of the tank and in layers near the bottom. The water layers may range from a fraction of an inch to several inches in thickness. In order to determine accurately the amount of product or stock in the tank, the quantity of water must be determined and this subtracted from the calculated amount of oil obtained by using an innage or outage bob, as hereinbefore indicated. It is very important that the amount of water is measured precisely. Even a small layer of water in a large tank or several tanks being inventoried for subsequent sale may reduce the actual volume of product being bought or sold by several thousands of barrels, resulting in substantial amounts of money in negotiating the sale.
In order to precisely determine location and thickness of the water layer, several chalks, paints, and pastes have been used to paint or cover the innage bob and lower end of the scale. The paint or chalk is brought into contact with the water when the innage bob is lowered to the bottom of the tank. The chalk, paint or paste is removed by water, or its color is changed, whereas the chalk, paint or paste is unaffected by the petroleum stock above the water. Thus the water level and quantity is readily determined at the same time that the product or stock height is taken.
Common bobs used in the above proceedure usually comprise a cylindrical brass bob six inches long which has a pointed bottom end and a flat top end with a perforated lug on the top or cap of the plumb bob for engagement with a swivel snap hook secured to the lower end of the tape. Bobs of this type are unsatisfactory for several reasons. For example, there is a critical area about the point of attachment where no readings can be taken directly because no calibrations are provided. The critical area extends from approximately the six inch to the eight inch calibrations. If the water level occurs in that region, the precise water level and thickness must be estimated, or a scale must be placed alongside the bob and tape to obtain the water reading. As another example, the bob tends to oscillate on the end of the scale causing the scale readings on the bob to be out of alignment with the scale readings on the tape. This tends to make it more difficult to find the water reading when the bob is removed from the tank.
There are several patents which disclose bobs designed to overcome the aforementioned problems.
Quist, U.S. Pat. No. 2,539,925 discloses an outgage bob of rectangular cross-section having an extended top portion provided with a laterally extending hook which receives a ring attached to the end of the tape measure. A spring clip secured to the body of the bob in operating engagement with the hook retains the ring on the hook. The ring is dimensioned to exactly extend the tape graduations whereby the graduations of the bob and tape are in exact prolongation of each other.
Quist, U.S. Pat. No. 2,580,320 discloses a liquid surface sensing bob comprising a hollow cylindrical body with a conical weighted section at the bottom. The body is filled with a discrete filler of low specific gravity and high reinforcing strength such as foam glass to maintain the shape of the bob under pressure. The bob in its preferred form has graduations from the juncture of the cylinder wall with the conical weighted section, and a flexible extension having a hook snap to which the ring of the measuring tape is attached. There is no provision for consecutive graduations about the point of attachment.
Johnson, U.S. Pat. No. 2,561,662 discloses a tank reading bob comprising an elongated body, a generally pointed cap, and a similar shaped base. The body is preferrably of square cross-section and has a hollow center of circular cross-section. The cap and base members are inserted into each open end of the body and locked into place by lock screws. The cap has a vertical slot which passes through it and extends through one side, and the upper end of the body has a similar slot with a transverse hole located at the bottom of the slot. The cap is rotated until the slots register and a tape measure is inserted therethrough into the bob and secured by a pin. After the tape has been secured, the cap is rotated so that the slots are out of alignment. Graduations are located on the outside of the base, body, and cap so that when the cap is rotated to lock the tape in the bob, the graduations form a continious-reading scale.
McDonald, U.S. Pat. No. 2,856,690 discloses a combination innage and outage liquid level gauge having a housing with a channel which receives an extensable slide. A lug extends from the housing for connecting the gauge to a measuring tape. There is no provision for consecutive graduations about the point of attachment.
Lewis, U.S. Pat. No. 1,680,297 discloses a plumb bob adapted for use with a metallic tape comprising a body formed in the shape of a frustrum of a cone split along its longitudinal center line into two portions having recesses to receive the tape, The two portions are fastened together arounr the tape by spring clips.
The prior art in general, and these patents in particular, does not disclose the present invention of a tank gauging bob adapted to be releasably attached to a measuring tape which comprises a generally cylindrical vertical elongated body having a measuring tape receiving lug and an extended portion which overlaps the lower portion of the tape and the point of attachment of the bob to the tape. The body and extended portion possessing graduations on their outer surface whereby when the tape is attached to the body, the graduations form a continious consecutive reading scale with the measuring tape.